Technical Field
The present invention relates to Group III nitride semiconductor devices that are prepared with spalling, and more particularly to GaN semiconductor devices provided with a protective cap layer that protects the Group III nitride semiconductor material during spalling and when preparing for spalling.
Description of the Related Art
Spalling may be employed to separate semiconductor materials from a substrate on which the semiconductor materials have been grown. With the mechanical forces involved in separating the materials by spalling, there are times when including a stressor layer among the stack of layers aids in separation by spalling. For example, some semiconductor materials exhibit relatively high fracture toughness and so it could be useful to include a stressor layer. Gallium nitride (GaN) is an example of a high-fracture toughness semiconductor material. Further, to assure good adhesion between the layers, an adhesion layer may also be included in the stack of layers prior to separation by spalling.
Sputtering may be employed in depositing an adhesion layer, such as a metal or metal-based adhesion layer. Sputtering may provide a metal or metal-based adhesion layer with stronger bonding properties when compared to other deposition methods, such as thermal evaporation. However, certain materials are not suited for receiving a sputter-deposited layer because the sputtering method can damage the deposit-receiving material. One such material is gallium nitride (GaN), and in particular, a GaN material that has been doped with a p-type dopant (“pGaN” or “p-doped GaN”). Exposure to the plasma during the initial stages of deposition may damage the surface of p-doped GaN, possibly to an extent that renders the p-doped GaN ineffective as a semiconductor material. For example, surface damage may render p-doped GaN non-conducting.